Generally, in a case of manufacturing a wing of an aircraft, wing elements such as spars, skins, and ribs are independently manufactured and the wing is assembled by joining these wing elements together with rivets, fasteners and the like. In the above-mentioned manufacturing of the wing elements and the above-mentioned joining of the wing elements, various types of machining is performed by using various types of machine tools to satisfy assembly precision of a completed wing.
For example, in Patent Document 1, a wing is assembled by joining two divided wing structures at the final stage. In the joining of the divided wing structures, flattening is performed on joining surfaces of the divided wing structures to improve surface accuracy in the joining surfaces.